Universal Dies Of Controllable Curvature

ABSTRACT

A flexible but strong universal die is disclosed, that is flexible enough to be elastically deflected into different curvatures by actuating forces and moments, while being strong enough to support the die forces and moments that it has to apply to parts to form them to the shape corresponding to its shape. A design of the die and actuation locations that makes it easy to deflect it into different constant curvatures, as well as into shapes with gradients of curvature along the length of the die, and the use of these dies for stretch roll forming are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application claims benefit and priority to U.S.patent application Ser. No. 13/565,793 entitled “Universal dies ofcontrollable curvature” and filed on Aug. 2, 2012 and U.S. Prov. Pat.Appl. No. 61/514,218 (EFS ID 10649019) entitled “Universal dies ofcontrollable curvature” and filed on Aug. 2, 2011 which is herebyincorporated by reference into the present disclosure.

BACKGROUND OF THE INVENTION Technical Field

The subject matter includes flexible but strong dies that can be used asdies for forming large extrusions, sheets and the like, of smallcurvature, the curvature of the dies being controllable by theapplication of much larger actuation forces and moments than the dieforces and moments arising from the forming process.

Background Art

Metal forming dies, such as dies used for stretch forming of extrusionsand sheets, are usually single monolithic pieces made of metals,plastics, wood, etc. The die geometry is fixed during the process offabrication of the die. The shape of the dies is imposed on the part bythe forming process. However, a separate die of the appropriate geometryis required for forming each part.

Recently, reconfigurable dies made up of an array of hydraulic cylinderswhich help define the position of the sheet are known. However, theseuse an interpolating layer of urethane which is flexible enough that itonly serves to smooth out the bumps that would be produced by thehemispherical surfaces on the ends of the cylinders. The interpolatinglayer is not strong enough to define the geometry over a free length,and support the forming loads experienced over this length.

BRIEF SUMMARY OF THE INVENTION

The universal dies disclosed here contain at least one “active area”whose curvature can be changed, and in addition, may contain otherlocators and guide surfaces for part guidance, actuators for forceapplication, etc. Each “active area” is made of one or more nestedlayers of strong but flexible beams or shells, preferably made of one ormore materials capable of sustaining high elastic (recoverable) limitingstrains without permanent (plastic) deformation such as Al 7075-T6,Titanium grade 5, PTFE, HDPE, polyimides, etc. Parts are either formedover the outer surface of the universal die or in between the outersurfaces of two mating pairs of universal dies with opposite (concaveand convex) curvatures. The outer surface may be covered with acompliant material, to compensate mismatch between the curvature of thedie and the part, and spread the die forces uniformly over the part. Inanother embodiment, the entire universal die may be circumscribed by abelt whose backing serves as a compliant material.

The curvature of “active areas” of these universal dies can be changedby the application of actuation forces and moments by externalactuators. The outer surface of the universal die may preferably have acurvature that is in the middle of the range of curvatures that the dieis expected to assume. The cross-section shape (especially thethickness) of each layer may be chosen according to the maximum changein curvature that is desired to be achieved/accommodated by elasticdeformation of the die elements. The number of layers may be chosenaccording to the maximum die forces and moments (also referred to as dieloads, which includes normal stresses and shear tractions) that arerequired to be supported by the universal die while forming the part.

For elongate parts that are predominantly bent in one plane, the activeareas could be lengths of beams made of materials with high elasticlimiting strains. For parts requiring to be bent to required curvaturesin two orthogonal planes, the active areas will comprise of shells madeof high elastic limiting strain materials, to permit changes incurvature of the die elements in two planes.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will now be described in detail with referenceto the following drawings.

FIG. 1: Schematic sketch of curvature adjustable universal die, with anactive length 110, cantilevered on one end 140 that is tangent to theincoming part, by fixation into a base plate 170, and actuated by anearly constant moment load on the other end. The long bending arm 150is used to translate the force exerted by actuator 130 into a constantmoment over the active length. Forces 120 exerted by the clamping actionand the belt tension are also shown. Note that the curvature of theactive length is expected to be smaller in SRF applications, but is hereshown exaggerated for clarity. (Drawing not to scale).

FIG. 2: Schematic sketch of the basic principle of action of anuniversal die in concert with a belt to apply traction to a part. Thebelt 250 is driven by drive pulley 260 around an outer die layer 220having an outer surface of die 210. One or more belt guides 160 are usedto guide the belt around sharp corners. Base 170 to which the actuatorsand one side of the flexible dies are fixed is also shown. The neutralshape of the die is convex (drawing not to scale)

FIG. 3: Schematic sketch of a concave universal die that would mate witha convex universal die. The belt 250 is driven by drive pulley 260around an outer die layer 320 having a concave outer surface 310(drawing not to scale)

FIG. 4: Two curvature controlled universal dies stretch bending anextrusion; the sketch is not to scale. The drawing shows first convexuniversal die 410 being clamped against second concave universal die 420by external actuators (clamping cylinders) 430. Brake station 460 brakesthe movement of extrusion 450. Note that the actual curvature of theuniversal dies will be smaller and the drive pulley will be smaller sothat there will be no interference between the formed part and thebelts. (Drawing not to scale)

FIG. 5: Use of a second actuator 520 directly on the active length ofthe die through compliant material 510, to support the clamping and beltforces 120. (drawing not to scale)

FIG. 6: Two opposing universal dies that are clamped together across theactive lengths (beams) by actuators (opposing clamping cylinders 610 and620) connected to the overall ground for the station, forming a station.The drive pulleys also serve as the tensioning pulleys. Note that thefree length of extrusion between the brake station and the tractionstation can be minimized to prevent unconstrained bending or buckling ofthe material in this length. Also note that the brake station can beanother station similar to the first one shown, in which the belts aredriven in directions opposite to those shown for the first station, topull the part (the extrusion) in the opposite direction

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows one possible design of a curvature controllable universaldie and a method for controlling the curvature of the same. Theuniversal die has a small active length 110 in the middle which engageswith the part to incrementally form it to the desired curvature. Asshown in the figure, the active length 110 is a curved beam made of astrong, but flexible, material (of high elastic limit strain beyondwhich plastic deformation sets in). The active length of the die isfixed (cantilevered) to a ground plate 170 on the right side such thatthe tangent to the active length at this point 140 is substantiallyhorizontal, along which the part being incrementally formed comes intothe die. The other end (the ‘free’ end) of the active length has a longbending arm 150 that permits application of a nearly constant momentload along the active length 110 of the beam. The die 110, cantileveredend 140 and long bending arm 150 could all be machined out of one pieceof metal with generous radii to avoid stress concentrations. In thefigure the die 110 is shown as having a nearly uniform section, so thatthe change in curvature everywhere along the length of the beam isconstant in response to a constant moment load. Note that the beam'sthickness to length ratio is very high, that such a beam would normallybe not thought of as a flexible beam. It can support substantial loads120 due to clamping forces, belt tension, etc., without substantialchange in curvature. The long bending arm 150 is acted upon by anactuator 130 that is also fixed to the ground plate 170 and is capableof applying substantial forces to deflect the active length 110 intodifferent curvatures. The actuator 130 applying the actuation force tothe long bending arm is positioned at an angle θ such that the momentarm decreases from the free end to the cantilevered end. This gradientof moment along the length of the beam cancels out the gradient ofmoment set up by the normal forces and tractions applied on the diesurface. It could also be the case that the beam can have a variablesection moment of inertia along its length to compensate for anyresidual (net) gradients in bending moment.

These universal dies 220, and belts sliding over these dies 250, can beused to apply normal and shear tractions to extrusions and sheets tosimultaneously stretch and form local regions to desired membranestretches and curvatures in the CNC stretch forming process that is alsoknown as Stretch Roll Forming. The advantage of these curvaturecontrolled universal dies is that the curvature can be adjusted to theappropriate value required to impart the required curvature to thecurrent region of the part that is being formed, and so these dies canbe used to apply tractions over a larger length of contact between thepart and the dies 110 (which is also the contact area per unit width ofthe belt). The larger contact length in turn permits proportionallylarger shear and normal fractions per unit width of belt to be appliedto the part by a single universal die/belt, since with strong belts(reinforced with fibers such as Kevlar) the limiting fraction stress ofthe coating (or matrix or backing) of the belt is the factor that limitsthe traction. For instance, if a belt with a working strength of1000N/mm width is used, if the working shear strength of the backing is14N/mm² (2 ksi), the contact length will have to be 1000/14=71 mm to usethe full capacity of the belt and transfer the maximum traction possibleto the part. This is not possible to do if there is a large mismatchbetween the curvature of the dies and that of the region of the partbeing clamped by the die (if the backing were compliant enough thiscould be doable, but it will then not be strong enough to sustain aworking shear strength of 14N/mm² like assumed above).

One possible design of a universal die with multiple nested dies isshown in FIG. 2 and FIG. 3. For ease of manufacture, this could be madeby cutting out the grooves shown between the nested dies using wire EDM,(if the surface finish is not fine enough, may need to possibly polishthe cut grooves using a process such as abrasive flow machining or coatthe grooves' surfaces with a thin lubricious coating layer such asPTFE), and then inserting strips of PTFE between the layers. Note that,as the location of one or more actuation points moves farther away fromthe die surface, the relative ratio of the bending moment to the shearforce increases, causing the curvature to become nearly uniform. Bychanging the location(s) and direction(s) of action of the actuation,the bending moment may be caused to increase or decrease along thelength of the die, causing the curvature to vary proportionately alongthe length of the die. By varying the thickness of each of the layers,the bending moment required to bend those layers can be made smaller,while the cumulative thickness helps support larger normal (clamping)stresses.

The neutral curvature is the curvature of the die in the unloadedcondition. A pair of dies would have opposite neutral curvatures asshown in FIG. 4, the magnitude of the curvatures being slightlydifferent to accommodate the required thickness of the part and the pairof belts applying tractions on both sides of the part.

The following calculations can be used to decide upon the thickness of amaterial that can be used for making the universal dies. Titanium grade5 (Ti-6Al-4V) has a yield strength of 1.1 GPa and elastic modulus of 114GPa. So its yield strain is of the order of 1%. Say the die has toaccommodate a range of radii from 30 inches to 84 inches.

0.01>Bendingstrain=t/2*(Δκ)=t/2*(1/r_(n1)−1/r_(n2))=t/2*(1/30−1/84)=t/2*0.021=t*0.0107which implies that 0.01>0.0107 t which implies that t<0.93 inch. If therange of curvatures can be smaller, or if the beam is deflected bothsides, starting from a base curvature of(κ₁+κ₂)/2=(1/30+1/84)/2=0.045/2=0.0226, i.e. a radius of curvature of44.2 inches, then the thickness can actually be double this. For thiskind of thickness, even just one strip will be sufficient to support allthe normal loads and shear tractions exerted by the belt+the clampingload on the die. The ratio R/c where R is the radius and c=Ymax (thedistance to the extreme fiber from the neutral axis) is about 40 for theabove numbers. From Roark's formulas for stress and strain (6^(th) Ed.,Pg. 236), it is clear that by the time R/c is more than 10, thedeviation from a straight beam is small.

The following is an example of a simplified calculation of thedeflection of the die due to the normal clamping stress, the belttension and the shear traction. Assuming that the die is clamped on oneside as shown in the figures, the bending moment due to forces 120 willbe greatest at the fixed/cantilevered end 140. Formula for max bendingmoment due to uniform normal clamping stress of 5000 psi (35 MPa), shearfraction of 500 psi (3.5 MPa due to a coefficient of friction of 0.1between the belt and the die, which can be neglected in comparison tothe normal stress), and a total belt force of 1000 N/mm (to beconservative assume that the belt force is applied at the tip of thebeam, perpendicular to the length of the beam). The max bendingmoment=1000*75+wL²/2=75,000+35N/mm²*75²mm²/2=75,000+196,875N-mm/mm=272,000 N-mm/mm width of belt. For a 1 mm wide belt and die, themoment of inertia is I=1/12*1*23³=1014 mm⁴/mm. E=114000 N/mm²; This maxbending moment will cause a max bending stress of S=(M/I)*Ymax=3.2 GPaand a change in curvature of Δκ=M/EI=272000 N-mm/mm/(114000N/mm²*1014mm3)=1/425 mm⇒R=0.4 m=16.7 inch. The stress is beyond yielding and thechange in curvature is quite significant.

The change in curvature can be substantially decreased by actuating thelong bending arm in two orthogonal directions, one of which issubstantially along the arm (the actuator shown using phantom lines inFIG. 1). The actuator along the length of the long bending arm can beused to oppose the belt loading and the distributed clamping force,substantially reducing the effect of these on the curvature of theactive length of the die—i.e. the “free” end will no longer be free, butbe “simply supported”. Another even simpler solution will be to use thesecond actuator 520 to directly support the active length of the die,either at an “Airy” point or via a compliant insert 510 (as shown inFIG. 5). This actuator will react the total clamping force and belttension. In fact, this actuator could be used to clamp the two pairs ofdies together (as shown in FIG. 6), without actuating the base plates onthe two sides in opposite directions (as in FIG. 4).

Change in curvature as well as the maximum stress can also be reduced bya factor of 8 by doubling the thickness of the beam, using the middlecurvature as the natural curvature, and using both sided actuation ofthe actuator. For beam thickness=46 mm, I=8112 mm̂4; Δκ=1/(8*425mm)=1/3.4 m=1/136 in. Max stress=400 MPa, well within the yield ofTi-6Al-4V.

This can be further reduced by making the fixed point the middle of thecurved die and deflecting both free ends equally. This will cause theeffect of the normal stress and the belt tension to be reduced by afactor between 2 and 4, without significantly affecting the flexibilityof the die. However, the whole die structure will have to be rotated tomake it tangential to the incoming extrusion—this will require a heavyrotary table bearing and a high torque drive.

The width of the beam can also be made twice the width of the belt—thiswill also further reduce the effect of these external loads. Note thatthe hydraulic actuator will need substantial force and stroke capacityto deflect these dies. For fixed dies such as those needed to build theT-section fuselage ribs for Cessna, one can even use a screw basedadjustment to adjust the curvature of the die to obtain the desiredcurvature of the parts.

Note that by appropriate design of the angle of the actuator (asmentioned below), one can get to a point where the position of theactuator can be directly related to the constant curvature of activesurface of the die. This will then be very easy to implement inpractice.

The angle at which the actuators apply the force can be changed so thatthe bending moment due to the actuator is highest at the free end 150and decreases towards the clamped end 140. This second variation can bemade to exactly counteract the first one (due to die loads 120) byorienting the cylinder appropriately, so as to cause the bending momentto be constant, i.e., the curvature of the die to be constant. Note alsothat the angle of application of the force can be varied to produce anydesired variation in curvature along the die surface. Also, instead ofvarying the angle, a second actuator at 90 degrees to each actuator canbe used to apply forces in two orthogonal directions. The plane ofaction of these two actuators can also be independently adjusted to beabove or below the centerline of the die to counteract the twistingmoment that will be caused by one another being off centerline, and anyother twisting moment one the die, for instance, due to the clampingforces being applied only along the bottom or along the top of theactive surface (curved portion) of the die, as will be the case when aT-section or L-section is being pulled by the flange (cap).

Feedback control of the die curvature can be accomplished based onmeasured part curvature.

FIG. 4 shows two complementary universal dies 410 and 420 at a station,that are used to stretch the length of a part 450 between the stationand a separate brake station 460 that opposes the tractions exerted bythe belts around the universal dies. If each of the two belts can apply1000N/mm traction to the part, assuming that the fraction of the C.S.area of the extrusion over which traction is applied (i.e. only cap ispulled on,; the leg is not pulled) is ½, this means that 1000N/mmtraction can be applied over the entire length of the part. For even7075-T7 parts, the Yield is about 75 ksi=516 Mpa, which implies thatnearly 2 mm thickness (0.08″) wall thickness of the extrusions can behandled in one stage itself.

Multiple stations similar to those shown in FIGS. 4 and 6 can be used toapply cumulatively larger tractions to parts. The maximum distancebetween successive stations should be small enough compared to theradius of curvature and the thickness of the segment of the part betweenthe stations so that the bending moment due to the stretch force withinthe work piece, that acts to further bend or unbend the section, issmall compared to the bending moment required to form the section to therequired radius of curvature. In between the brake station and the firsttraction station, where the stretch force is high enough to plasticallydeform the part in tension, only a small bending moment is required toform the part. This small bending moment is provided by a smalldifference in the normal force applied by the two opposed universal diesat the first traction station and the bending to the curvature occurs atthe inlet to the first traction station as shown in FIG. 6. Bycontrolling the curvature of the universal dies, as well as thetractions applied by the belts, controlled curvatures can be imparted tothe part in both orthogonal planes containing the length of the incomingpart as well as a twist about the longitudinal axis of the part. In thecase of all the prior art, tractions are exerted between stations whichare substantially displaced along the length of the part. If forming ofthe part to a curvature were to be attempted with such stations, itwould actually cause the part to get straightened out—i.e., the stretchforce between stations would straighten the bent part. This is the casebecause the size of the rolls needs to be high in order to apply thesubstantial normal and traction forces required in one station. Withoutthe use of progressive buildup of the tractions via a number of smallrollers and/or traction elements, which serve to increase the stretchforce while eliminating the bending moment that tends to straighten outthe part, stretch forming to deterministic contours is impossible. Thedistance between the stations should in general be not more than a fewtimes the depth dimension of the profile. In all prior art where eithera sweep or a curvature in the plane have been claimed, this is achievedonly by bending, not stretch bending.

Even if a total contact length between the belt and the extrusion of 6″instead of 3″ were used (i.e. a factor of safety of 2.0 to ensure thatthe traction can be transferred from the belt to the extrusion withoutslipping at the interface), a single well supported flexible die as inFIG. 6 may be sufficient. Otherwise 2 or 3 layers of flexible dies canbe used to help take up the normal stresses as shown in FIG. 4.

Another approach is to apply clamping forces on the web (or stem or leg)that remains flat and apply traction to it while using a flexible die toguide the extrusion and the belt along the instantaneous curved path ofinterest.

If sand particles or steel shot were included into the elastomer orpolymeric coating of the belt, this will help impart a shot-peenedfinish to the extrusion that industry can readily recognize and accept.The indents will also increase the traction that can be transmitted tothe extrusion at lower clamping forces. Metallized fibers can be used toproduce woven endless belts, which will have a higher friction to thepart. This will also permit the use of a smaller clamping stress.

Woven endless belts with Kevlar reinforcement and polyimide or otherhigher temperature resins as the matrix will allow hot forming of theparts (sheets/extrusions). This may also increase the frictioncoefficient. Hot forming allows the material to deform more withoutcracks developing (either macroscopic cracks, or micro-cracks bymechanisms such as precipitate shearing), which will help preserve thefatigue life even for parts requiring large deformations. In-processheating of the part being formed (for instance, using heated rollerstouching the extrusion in between the brake and the first tractionstation), and cooling the part immediately beyond the forming region(i.e. the first traction station) will minimize undesirablemetallurgical changes.

The greatest benefit of incremental forming for aerospace applicationsis the ability to control the stretch to be uniform or vary in apre-determined manner all over the part. A 5% uniform stretch willdecrease the weight per unit length by 5%. Further, if this stretch ledto work hardening of the material by 5%, the total weight saving will be10%.

Parts may also be alternately compressed and stretched so the geometrydoes not change much, but the strengthening is significant, since theequivalent strain is cumulative. Note that the free length between thedie and the brake station, in which forming happens, can be minimized,permitting significant compression without danger of buckling. This mayalso lead to highly workhardened product, such as is the goal of severeplastic deformation processes (such as ECAE), and can produce very smallgrain size materials, leading to much higher strength and significantweight reduction.

In order to carry out feedback control of the process, the machine caninclude one or more models of the stretch forming process that take thematerial type, properties, profile of the cross-section etc. as inputsand predict the amount of springback, and use this to set the diecurvature required in order to get the finished radius desired. Themachine can also have a radius monitoring method (using three or morepoint-position sensors or a line-scan sensor to sense the profile over alength from which the average radius of curvature of the profile can becalculated. This will have to be done at the exit of the extrusion whenspringback has occurred). If the measured springback is different fromthe model value, the model can then updated. Update can occurinstantaneously and be effective during the formation of the rest of thefirst extrusion itself or it can be applied from the next part onwards.Model update can also use the actual properties measured (based on thetorque required for a given amount of stretch). The model can also beused to compute settings for re-work of parts to fine-tune thegeometry—if the first pass did not get to the exact geometry because ofspringback, deviations from expected and actual radii can be used torecalculate the new forming radius and reform the part to the requiredradius with a minimum amount of additional stretch. This will beespecially useful for high cost materials and high value parts.

The frictional torque can be measured during a tuning process, when apart is gripped and moved back and forth without any brake (stretch)force. Since there is no stretch force, the only force the system isworking against is friction. This testing can be used to build acomprehensive model for friction as a function of operating conditions,such as belt tension and die curvature.

For measurement and documentation of the strength as a function ofposition along the extrusion, it is better if a continuous loop ofroller bearings were used between the die and the belt—as this willreduce the friction component of the torque and make it moreconsistent—the friction will be independent of the torque or the stretchforce exerted at a station. The machine, with feedback control of themotor torques to maintain speed and stretch constant, and preferablyusing rolling elements at all possible locations to decrease friction,can actually be used to record the stretch of each station, as well asto record the load required to stretch that section to 3%; i.e. themachine also acts like a high resolution UTM (especially if frictionbetween the belts and the dies is minimized), noting the stress for acertain strain at each length of the extrusion.

This can be used to measure the stress-strain curve of an initial lengthof the extrusion coming in, wherein the extrusion is “locked” in placeat the inlet side encoder and the stress-vs. strain curve is measured byslowly stretching so the measurement of the outlet side encoderincreases. Using the measured stress-strain curve, and models for thebending moment and springback, the expected bending moment andspringback at any point of the extrusion can be estimated based on thecurvature at that location.

The model can include the bending moment caused by the distance betweenthe stretch force application region (for instance, the flange) and thecenter of inertia of the section through which the stretch force has topass for pure stretching. The models can be refined by constantlymeasuring the actual curvature produced and comparing with the curvatureestimated from the model and using this to update parameters in themodel. Bayesian updating can be used with the current model parametersas priors to reduce the sensitivity of this update to noise.

A model for belt contact stiffness changes (for instance, due to slowdegradation of the belt over time) can also be derived based on theresponse of the belt to torque or the belt compression measured duringclamping at different forces without any extrusion in between.

Additional Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown and described. However, the present inventor alsocontemplates examples in which only those elements shown and describedare provided.

All publications, patents, and patent documents referred to in thisdocument are incorporated by reference herein in their entirety, asthough individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls. Inthis document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims.

Also, in the above detailed description, various features may be groupedtogether to streamline the disclosure. This should not be interpreted asintending that an unclaimed disclosed feature is essential to any claim.Rather, inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description, with each claim standing onits own as a separate embodiment. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1. A forming process comprising: forming a part around one or more firstuniversal dies, by a means applying forming force, to take a shapesimilar to that of the one or more first universal dies, wherein the oneor more first universal dies contain one or more active areas whosecurvatures can be changed while the part is being formed andsimultaneously moved along the one or more active areas, wherein thechange in curvature is accomplished by use of one or more actuators tocause actuating forces and moments at the active areas that are morethan die forces and moments at the active areas, that are caused by theforming force, wherein the one or more actuators act either overportions of the active areas, or over other regions of the one or morefirst universal dies.
 2. The forming process of claim 1 wherein theforming force is reduced by stretching the work piece along its length.3. The forming process comprising: forming a part by means of one ormore first universal dies to take a shape similar to that of the one ormore first universal dies, wherein one or more second universal dies ofshape that mate with the one or more first universal dies is providedwherein the one or more first universal dies and second universal diescontain one or more active areas whose curvatures can be changed whilethe part is being formed and simultaneously moved along the one or moreactive areas, wherein the change in curvature is accomplished by use ofone or more actuators to cause actuating forces and moments at theactive areas that are more than die forces and moments at the activeareas, that are caused by the forming force, wherein the one or moreactuators act either over portions of the active areas, or over otherregions of the one or more first universal dies wherein the means ofapplying forming force acts through the one or more first universaldies, the one or more second universal dies, or a combination thereofsuch that the part is clamped between the one or more first and seconduniversal dies to form the part to a local curvature of the one or morefirst and second universal dies, the one or more first and seconduniversal dies and the means of applying forming force togethercomprising a station.
 4. The forming process of claim 1 or claim 3wherein the one or more first universal dies, and the one or more seconduniversal dies, when provided, have a compliant material over it/them soas to apply traction to the part and to accommodate mismatch in thecurvatures of the mating dies.
 5. The forming process of claim 4 whereinthe one or more first universal dies and second universal dies, whenprovided, are circumscribed by a respective endless belt withelastomeric backing that serves as the compliant material.
 6. Theforming process of claim 5 wherein the belts are driven in oppositerotational directions around each of the one or more first and seconduniversal dies of a station, so that the belts at a station togetherpull the part in one direction.
 7. A forming process using in series twoor more stations of claim 4, the curvatures of each of the active areasof which are changed to form one or more local shapes at differentlocations along the length of the part, to form the part to the desiredcurvature at each of these locations.
 8. The forming process of claim 7wherein the part moves through the series of two or more stations, eachof which adjusts the curvatures of each of the active areas of the oneor more first universal dies or first and second universal dies, tocorrespond to the local shape required to form area of the part incontact with each of the active areas.
 9. The forming process of claims8 wherein the two or more stations pull the part in opposing directionsto generate longitudinal stress within the part.
 10. The forming processof claim 9 wherein bending of the part by the two or more stations isassisted by substantial longitudinal tensile stress within the part,which reduces the bending moment required to plastically bend the part.11. The forming process of claim 9 wherein bending of the part by thetwo or more stations is assisted by substantial longitudinal compressivestress within the part, which reduces the bending moment required toplastically bend the part.
 12. The forming process of claim 10 whereinthe stations are arranged into two sets, a set of exit stations thatpull the part through, and a set of brake stations that apply anopposing force to the part as if to try to prevent the part from beingpulled through the set of brake stations.
 13. The forming process ofclaim 12 wherein the part enters at the beginning of the first brakestation and exits at the end of the last exit station.
 14. The formingprocess of claim 13 wherein changes in curvature of each local region ofthe part occur during the time the local region of the part is withinthe first exit station.
 15. The forming process of claim 14 wherein theposition and orientation of each of the exit stations is changed toplace these stations at the correct locations and orientationsdetermined by the already established shape of the part, so that theycan pull the part without further deformation.
 16. The forming processof claim 6 wherein said belts have harder fibers and/or particlesembedded in the elastomeric backing, to introduce additional localsurface deformation of part, to produce surface finish or propertiessimilar to that of shot peened parts.
 17. The forming process of claim 5wherein the interfaces between the belt(s) and the universal diescontains low friction lubricants that reduce friction between the diesand the belt(s).
 18. The forming process of claim 6 wherein rollingelements are interspersed between the belts and the universal dies toreduce friction between the universal dies and the belts.
 19. A formingprocess comprising: forming a part around one or more first universaldies, by a means applying forming force, to take a shape similar to thatof the one or more first universal dies, wherein the one or more firstuniversal dies contain one or more active areas whose curvatures can bechanged while the part is being formed and simultaneously moved alongthe one or more active areas, wherein the change in curvature isaccomplished by use of one or more actuators to cause actuating forcesand moments at the active areas that are more than die forces andmoments at the active areas, that are caused by the forming force,wherein the one or more actuators act either over portions of the activeareas, or over other regions of the one or more first universal dies,wherein the means of applying forming force acts through a matching setof second universal dies of shapes that mate with the previously saidone or more first universal dies to form a first station where the partis clamped between the one or more first and second universal dies toform the part to the local curvatures of the one or more first andsecond universal dies, wherein the one or more first and seconduniversal dies are each circumscribed by endless belts that are drivenaround the dies along the active areas, and where a second station actson the part and has endless belts driven so as to pull the part in adirection opposite the direction the part is moved by the first station,to generate longitudinal stress within the part that reduces the bendingmoment required to plastically bend the part.
 20. The forming process ofclaim 1 wherein the one or more first universal dies, and the one ormore second universal dies, when provided, have a compliant materialover it/them so as to apply traction to the part and to accommodatemismatch in the curvatures of the mating dies.